1. Field of the Invention
The present invention relates to an object, a method, or a manufacturing method. The present invention relates to a process, a machine, manufacture, or a composition of matter. In particular, one embodiment of the present invention relates to a semiconductor device or a method for manufacturing a semiconductor device.
In this specification, a semiconductor device generally means a device that can function by utilizing semiconductor characteristics. A display device, an electro-optical device, a semiconductor circuit, and an electronic device may include a semiconductor device.
2. Description of the Related Art
Attention has been focused on a technique for formation of a transistor using a semiconductor thin film formed over a substrate having an insulating surface. The transistor is used in a wide range of electronic devices such as an integrated circuit (IC) and an image display device (display device). A silicon-based semiconductor material is widely known as a material for a semiconductor thin film applicable to a transistor, and in addition, an oxide semiconductor has been attracting attention.
For example, Patent Document 1 discloses a transistor including an amorphous oxide semiconductor film containing indium (In), gallium (Ga), and zinc (Zn).
Patent Documents 2 and 3 disclose techniques for improving carrier mobility by stacking oxide semiconductor films.
A transistor including an oxide semiconductor film to have an extremely low leakage current in an off state. For example, a CPU with low-power consumption utilizing the low leakage current of the transistor including an oxide semiconductor film is disclosed (see Patent Document 4).